Tonight on The Last Word: Judge Aileen Cannon officially dismisses Trump's lawsuit against DOJ. Plus, Neal Katyal on his "masterful" oral argument before the Supreme Court in an important elections case. Also, Sen. Kyrsten Sinema changes her party voter registration from Democrat to Independent. And the ‘Lost Tapes' of Nelson Mandela are released. Barbara McQuade, Glenn Kirschner, Neal Katyal, and Rick Stengel join Lawrence O'Donnell.